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Measuring effective electro-optic coefficient at 1040?nm by spectral intensity modulation with THz time-domain spectroscopy
摘要： We report a single method for measuring the e?ective electro-optics (EO) coe?cient only by spectral intensity modulation with a terahertz time-domain spectroscopy (THz-TDS) device. Compared with conventional methods, the measuring device based on THz-TDS by probing the spectral intensity modulation is simple, rapid, and highly sensitive. It does not require special preparation process, electrode contact or applying high voltage on the sensor samples. The EO coe?cients of four kinds of materials, namely, ZnTe and GaP crystals, DAST wafer and GaSe ?lm, are measured at 1040 nm. The results showed good agreement with literature data by the conventional methods.
关键词： E?ective electro-optic coe?cient,EO materials,Spectral intensity modulation,THz-TDS
更新于2025-11-28 14:24:03
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Polarized THz Emission from In-Plane Dipoles in Monolayer Tungsten Disulfide by Linear and Circular Optical Rectification
摘要： Recent advances in the development of polarized terahertz (THz) emission from nanomaterials have not only opened up a new “TeraNano” interdiscipline but also provided a new tool for nonlinear optical process research. Herein, THz radiation mechanism of monolayer tungsten disulfide (WS2) is first investigated by both linear and circular polarization laser excitations at room temperature. The results reveal that polarized THz emission is dominated by the optical rectification based on in-plane nonlinear dipoles, which is totally different from that of bulk WS2. The mechanism is verified by the azimuthal angle and pump polarization angle dependence of THz emission in both experiment and theory. Furthermore, controllably elliptically polarized THz emission is observed with the maximum ellipticity of ≈0.52 based on nonresonant nonlinear process under the circularly polarized excitation. A clear understanding of THz radiation mechanism of 2D materials will facilitate further design, optimization, and polarization control of integrable 2D THz optoelectronics.
关键词： THz radiation,monolayer WS2,in-plane nonlinear dipoles,optical rectification,elliptically polarized THz emission
更新于2025-09-23 15:23:52
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Orientation-Dependent THz Response of <i>m</i> -Plane Sapphire Substrate by Polarization-Sensitive THz Time Domain Spectroscopy
摘要： The dielectric response of m-plane sapphire (m-sapphire) substrates in the terahertz (THz) frequency is investigated using polarized-sensitive femto-second THz time-domain spectroscopy. We examined the transmitted THz time-domain waveforms with respect to the parallel-polarized THz field by rotating phi angle of m-sapphire substrates. The THz amplitude significantly decreased at the azimuth angle of 0°, 90°, and 180° with roughly equal amplitudes and no propagation time delay. The time delay of 480 fs in the THz pulse oscillations was observed between the azimuth angle of 45° and 90°, possibly due to the birefringence of nonpolar m-sapphire substrate. Strong THz field absorptions around ～1 THz frequency at azimuth angles of every 90° could be attributed to low-frequency phonon modes.
关键词： Sapphire,Birefringence,Time-Domain Spectroscopy,THz
更新于2025-09-23 15:23:52
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Transmission Low-Frequency Raman Spectroscopy for Quantification of Crystalline Polymorphs in Pharmaceutical Tablets
摘要： The purpose of this study was to quantify polymorphs of active pharmaceutical ingredients in pharmaceutical tablets using a novel transmission low-frequency Raman spectroscopy method. We developed a novel transmission geometry for low-frequency Raman spectroscopy and compared quantitative ability in transmission mode versus backscattering mode using chemometrics. We prepared two series of tablets: 1) containing different weight-based contents of carbamazepine form III and 2) including different ratios of carbamazepine polymorphs (forms I/ III). From the relationship between the contents of carbamazepine form III and partial least squares (PLS) predictions in the tablets, correlation coefficients in transmission mode (R2= 0.98) were found to be higher than in backscattering mode (R2= 0.97). The root mean square error of cross-validation (RMSECV) of the transmission mode was 3.9 compared to 4.9 for the backscattering mode. The tablets containing a mixture of carbamazepine (I/ III) polymorphs were measured by transmission low-frequency Raman spectroscopy, and it was found that the spectral shape changed according to the ratio of polymorphs: the relationship between the actual content and the prediction showed high correlation. These findings indicate that transmission low-frequency Raman spectroscopy possess the potential to complement existing analytical methods for the quantification of polymorphs.
关键词： Transmission,Carbamazepine,Pharmaceutical Tablets,Quantification,Low-Frequency Raman Spectroscopy,THz-Raman,Crystalline Polymorph
更新于2025-09-23 15:23:52
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Angular streaking of Auger-electrons by THz field
摘要： Rotational streaking by a circularly polarized THz field of Auger electrons generated by a short extreme ultraviolet (XUV) or X-ray pulse is theoretically investigated. The character of the streaking pattern depends on three main parameters: the duration of the XUV pulse, the Auger decay time-of-life and the period of the THz field. Different cases with various interrelations of these parameters are discussed. Examples of the patterns are calculated within the strong field approximation. Correspondence between the angular streaking of electrons in the processes of photoionization and Auger ionization is considered. Retrieval of the Auger decay parameters from circular streaking spectrum is discussed.
关键词： THz field,strong field approximation,Auger electrons,angular streaking,ultrafast processes
更新于2025-09-23 15:23:52
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[IEEE 2018 IEEE Asia-Pacific Conference on Antennas and Propagation (APCAP) - Auckland (2018.8.5-2018.8.8)] 2018 IEEE Asia-Pacific Conference on Antennas and Propagation (APCAP) - Performance Enhancement Of Cmos Terahertz Detector
摘要： For improving the performance of CMOS terahertz detectors, parasitic capacitance reduction technique and new working model are proposed for MOSFET devices. We investigate the influence of source parasitic capacitance and drain-to-source current on the performance of CMOS terahertz detectors and analyze the relationship to the voltage responsivity (RV) and noise equivalent power (NEP) of detectors. Experiment on the CMOS detectors with a 650GHz antenna shows the maximum improvement of voltage responsivity can attain to 155% by suppressing gate-source parasitic capacitance. The additional drain current Ids can further increase RV while NEP remains unchanged.
关键词： Antenna,CMOS THz detectors,DC current,Voltage response
更新于2025-09-23 15:23:52
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Precoding and Detection for Broadband Single Carrier Terahertz Massive MIMO Systems Using LSQR Algorithm
摘要： The terahertz (THz) communication utilizes the frequency spectrum above 300 GHz and is widely considered as a promising solution to the future high-speed short-range wireless communication beyond millimeter wave (mmWave) communication. While providing tens of gigahertz bandwidth, it is subjected to high propagation path loss, inter-symbol and inter-user interferences. The massive multiple-input-multiple-output (MIMO) can be applied to address these problems by cooperation between many access point (AP) antennas. However, the THz channel characteristics, including high propagation path loss, frequency selectivity and big number of samples per channel impulse response (CIR), require carefully tailored algorithm for massive MIMO signal processing. In this paper, we propose a single carrier minimum mean square error (MMSE) precoding and detection algorithm for frequency selective THz channels. The MIMO signal transmission is described with the block matrices. A gain control heuristic is introduced to reduce the complexity. The sparsity property of the channel is utilized to construct sparse channel matrices and the least square QR (LSQR) algorithm is applied to efficiently solve the problems. Besides the uniform antenna array, the hybrid array consisting of several subarrays is considered as well. Simulation results show that the massive MIMO array can provide a satisfactory performance in terms of bit error rate (BER).
关键词： detection,massive MIMO,frequency selective channel,precoding,LSQR algorithm,block matrix,minimum mean square error,THz communication
更新于2025-09-23 15:23:52
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[IEEE 2018 AEIT International Annual Conference - Bari, Italy (2018.10.3-2018.10.5)] 2018 AEIT International Annual Conference - Solid State Rectifier as Terahertz Detector
摘要： We present a new solid state rectifier, compatible with CMOS integrated circuit, suitable to direct conversion of terahertz radiation, at room temperature. The structure creates a rectenna, consists in a truncated conical helix extruded from a planar spiral and connected to a nanometric metallic whisker at one of its edges. The whisker reaches the gate of a MOS-FET transistor. Rectification can be obtained by the self-mixing effect occurring into the plasma waves generate underneath the gate. The proposed solution is easy to integrate with existing imaging systems. No need of scaling toward very scaled and costly technological node is required, since the plasma wave are not dependent on the gate extension. The remaining electronics should only provide the necessary integrated readout. A theoretical explanation of the self-mixing process, and TCAD simulations showing the onset of the DC potential are presented. An additional detector structure, the double barrier rectifier, is also presented for comparison.
关键词： MOS-FET,rectifying antenna (rectenna),Image detector,CMOS,THz antennas
更新于2025-09-23 15:23:52
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[IEEE 2018 25th International Conference "Mixed Design of Integrated Circuits and System" (MIXDES) - Gdynia, Poland (2018.6.21-2018.6.23)] 2018 25th International Conference "Mixed Design of Integrated Circuits and System" (MIXDES) - Study of Wireless Communications Link at Subterahertz Frequencies Using FET-based Detectors
摘要： This paper focuses on the wireless link development deploying (sub)THz waves. The article describes authors’ initial approach to the research and experiments dealing with THz communications. Presented work summarises the theory and achieved results in a ?led of FET-based THz detectors and readout circuits aimed at wireless THz data transmission. Our main goal was to provide proper data transmission utilising (sub)THz carrier wave — this has been experimentally achieved at 170 GHz and 289 GHz.
关键词： THz,data transmission,FET-based detectors,wireless communications
更新于2025-09-23 15:23:52
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Resonant Enhancement of THz Radiation Through Vertically Aligned Carbon Nanotubes Array by Applying Wiggler Magnetic Field
摘要： The present analysis develops a novel theory of terahertz radiation generation by beating of two laser beams, incident obliquely on the array of vertically aligned carbon nanotubes (CNTs) in the presence of an external wiggler magnetic field. The array of CNTs behaves as nanoantenna to generate THz radiations. The incident lasers exert a ponderomotive force on the electrons of the CNTs to produce nonlinear oscillatory velocity, which beats with the applied wiggler magnetic field. This beating produces a nonlinear current at (ω2 ? ω1, k2 ? k1 + k0) which acts as an antenna to produce the THz radiation. We observe that when the beat frequency (ω2 ? ω1) lies near the effective plasmon frequency of the CNTs, strong THz radiation is produced due to a resonant interaction of the laser with CNT electrons. The externally applied wiggler magnetic field enhances the efficiency of THz radiation of nanoantenna by providing the necessary momentum to the generated THz radiation. We explore the impact of radius and length of nanotubes on the efficiency of THz generation. The generated THz power is enhanced at an optimum angle of incidence of lasers with an array of CNTs.
关键词： THz radiation,Carbon nanotubes,Antenna theory,Wiggler magnetic field,Plasma,Nanotechnology
更新于2025-09-23 15:23:52